This invention relates to a rotary transformer, and more particularly to a rotary transformer which can solve the problems associated with rotary transformers having channel grooves machined therein, which typically experience a high percentage of defective parts and low dimensional precision.
As shown in FIG. 1, a rotary transformer used for transmitting signals received from heads to a stator side circuit in an apparatus having rotating type magnetic heads, such as a VCR, camcorder, or digital audio tape recorder, includes a stator side core and a rotor side core, each of which cores has channel grooves 3 corresponding to the number of channels and short ring grooves 4 each for inserting a short ring.
The rotor 2 and the stator maintain a very small aperture on the order of a few tens of .mu.m between them, and the rotor 2 reads signals from the heads while being rotated, and transmits the signals to the stator 1.
Therefore, the dimensions of the rotor 2 and the stator 1 should be very precise, otherwise picture quality can be degraded due to noise caused in the course of the signal transmission and due to fluctuation in inductance.
A method for forming the rotary transformer having the foregoing structure is as follows.
First, inside and outside diameters of the cylindrical ferrite powder sintered bodies shown in FIGS. 2a and 2b are formed with a powder molding method so as to have about 1 mm machining allowance taking into account of many steps of machining.
Outside surfaces of the formed cylindrical sintered bodies are primarily ground with a centerless grinder, and the inside surfaces are rough ground with an internal grinder taking the ground outside surfaces as reference surfaces. The outside and inside surfaces are finally ground with a special purpose grinder.
By machining the channel grooves 3 and the short ring grooves 4 in the inside and outside surfaces of the machined cylindrical ferrite sintered bodies according to a number of required channels, the cores shown in FIGS. 3a and 3b are completed.
However, since the rotary transformer having the foregoing structure is formed by machining the channel grooves and short ring grooves after grinding surfaces of the cylindrical ferrite sintered bodies, it has problems in that it has a high percentage of defective and low preciseness of the dimension of the channel grooves due to the machining.
Further the rotary transformer has problems in that the productivity has been low since the core has been machined one by one in each machining, and the machining has been difficult in case diameter of the core is very small in the order of a few millimeters.